Continuous Deployment (CD) is a deployment strategy where code changes are automatically deployed to production after passing automated tests. It enables rapid and reliable software delivery, ensuring that new features and bug fixes are quickly available to users.

The commonly used command to create a new migration for ASP.NET Core Identity changes is 'dotnet ef migrations add'. This command generates a new migration file containing the necessary SQL scripts to update the database schema based on changes in your Identity-related code.

In SignalR, a "Hub" is used to describe a group of connections that can be broadcast to. Hubs provide a high-level API for organizing connections and managing communication between clients and the server in real-time applications.

ASP.NET Core's primary advantage in this scenario is its cross-platform compatibility. It allows you to develop a web application that seamlessly runs on both Linux and Windows without the need for codebase modifications. This flexibility is especially valuable when targeting multiple platforms and ensuring a consistent user experience across them.

One of the core features of ASP.NET Core Identity is its ability to provide two-factor authentication (2FA). This adds an extra layer of security by requiring users to provide two forms of identification, typically something they know (password) and something they have (e.g., a mobile app-generated code) when logging in.

In the MVC (Model-View-Controller) design pattern, the Controller is primarily responsible for handling user input and interactions. It receives user requests, processes them, interacts with the Model to retrieve or manipulate data, and determines the appropriate View to render as a response.

The Identity middleware in ASP.NET Core primarily handles authentication. It intercepts requests to determine if a user is authenticated and provides features like cookie-based authentication, token-based authentication, and integration with external identity providers (e.g., Google, Facebook) for user login.

The primary language used for coding in ASP.NET Core is C#. While ASP.NET Core supports multiple languages, C# is the most commonly used language for building ASP.NET Core applications due to its strong integration with the framework and extensive tooling support.

To restrict access to registered users only, you would use the [Authorize] attribute. This attribute can be applied at the controller or action level and ensures that only authenticated users can access the specified resources. It doesn't require specifying roles, as it already implies authenticated users. [AllowAnonymous] would allow both anonymous and registered users, while [Authorize(Roles = "Admin")] and [Authorize(Roles = "User")] are role-based authorizations and are not suitable for this scenario.

In ASP.NET Core, JSON, XML, and Environment Variables Configuration Providers are default providers for configuration settings. However, Database Configuration Provider is not a default provider. Developers typically use it when they need to store configuration settings in a database.